Safety device

ABSTRACT

The invention related to a safety device for detachably locking the output member of a linear drive, comprising:a coupling rod coupled with the output element of the linear drive,a blocking unit, linearly movably penetrated by the coupling rod which is relatively movable with respect to the housing between a locking position blocking the stroke of the coupling rod and a release position enabling the linear movement of the coupling rod,a spring device for prestressing the blocking unit in the blocking position,a locking device for locking the blocking unit in the release position, wherein the locking device has locking rolling elements accommodated in the housing and a support sleeve which is linearly movably penetrated by the coupling rod,an electromagnet device that holds the support sleeve in the support position against the recoil force of at least one trigger spring or device.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the National Stage (§ 371) of International Application No. PCT/EP2019/078590, filed Oct. 21, 2019, which claims priority of German Application Serial No. 10 2018 218 642.1, filed Oct. 31, 2018, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to a safety device for detachably locking the output member of a linear drive.

BACKGROUND OF THE INVENTION

Certain safety devices have been known for a long time and are used as fail-safe devices to hold the output member of a linear drive in cases of power failure, for example, to hold the spindle of a process valve in a defined position, in other words, to lock it there. In a process valve, such a defined position may be, for example, the open position or the closing position of a valve member coupled to the spindle.

For example, in DE 2007 032 327 B3, a valve positioning device having a safety function is disclosed, wherein a safety device is switched on between the drive of the process valve and the valve member. The safety device has an electromagnet that blocks a piston when energized, allowing the normal operation of the valve spindle for opening, closing and freely controlling (without a spring) of a through opening on a valve fitting by means of a valve member coupled to the spindle. In the event of a power failure, the electromagnet is deactivated, and the piston is blocked, which causes the valve spindle to move into a safety position, which in this case is the closed position, regardless of the position of the pistons.

SUMMARY OF THE INVENTION

The object of the invention is to provide a safety device for detachably locking the output member of a linear drive with the help of which the connected system can be transferred safely to a predefined safety state.

The safety device according to the invention for detachably locking the output member of a linear drive comprises:

-   -   a coupling rod that is compatible with the output member of the         linear drive,     -   a housing which is linearly movably penetrated by the coupling         rod,     -   a blocking unit which is linearly movably penetrated by the         coupling rod, which blocking unit is relatively movable with         respect to the housing between a blocking position, which blocks         the stroke of the coupling rod, and a release position, which         allows the linear movement of the coupling rod.     -   a spring device for prestressing the blocking means in the         direction of the blocking position,     -   a blocking device for locking the blocking unit in the release         position, wherein the blocking device has locking rolling         elements accommodated in the housing and a support sleeve which         is linearly movably penetrated by the coupling rod, wherein the         support sleeve is movable between a support position, in which         the support rolling elements are held radially to the outside in         locking engagement with the blocking unit, and a release         position, allowing a retracting of the support rolling elements         radially to the inside, out of the engagement with the blocking         unit,     -   an electromagnet device which, when energized, holds the support         sleeve in the support position in the opposite position of the         force of at least one trigger spring of a spring device, such         that in the event of a power failure, the holding function can         be reversed and the support sleeve is moved by means of at least         one release spring into the release position whereby the         blocking unit can be transferred to the blocking position by         means of the spring device.

The safety device thus works on the basis of the cooperation of the electromagnet device with the locking device and the support rolling elements. In the release position, the blocking device is locked and inactive, such that the output member of the linear drive and the coupling rod connected to it are movable within their lifting range. In the event of a power failure, the blocking device triggers by removing the locking of the support rolling elements. The spring device then brings the blocking device into the blocking position, in which the lifting movement of the coupling rod is blocked. The safety device works purely mechanically, i.e. electrical auxiliary energy or other non-electrical auxiliary energy, such as for example compressed air, is not necessary for the function of the safety device. This guarantees that the safety device works reliably in case of failure.

In the further development of the invention, a stop is formed at the coupling rod and a counter-stop is formed at the blocking unit, said stops being arranged in the release position with an axial distance to each other that determines the stroke of the coupling rod and which are attached to each other in the blocking position causing the blocking of the output member.

In a particularly preferred embodiment, the blocking unit has a blocking sleeve penetrated by the coupling rod, which supports the blocking rolling element in the release position radially to the outside and holds said blocking rolling element in the locking position.

Conveniently, the blocking sleeve has an annular receiving space, in which an assigned support rolling element is immersed in the locking position.

In a further development of the invention, a plurality of support rolling elements grouped around the circumference of the support sleeve is provided, each having at least one support rolling element. In a particularly preferred embodiment, the support rolling element groups each have a plurality of support rolling elements arranged successively in the radial direction. Thus, when releasing the locking device, the support rolling elements can be used to bring said support rolling elements into the blocking position, to roll past each other and thus allow a quick and technically easy to implement removal of the locking system. Furthermore, the support rolling elements of the respective support rolling element group can easily be brought into the locking position, whereby rolling past each other is no longer possible, thereby locking the blocking unit.

Conveniently, the support rolling elements of a respective support rolling element group are staggered on top of each other in the release position of the support sleeve in the height direction. The radial extension of the support rolling elements within a support rolling element group is greater in the locking position of the support sleeve, i.e. greater in the locking position than in the release position of the support sleeve, wherein the staggering in the height direction causes a reduction of the radial extension.

In a further development of the invention, the support sleeve has an external wall on which a support sleeve, which interacts with the receiving space of the blocking device in the locking position, is formed, in which a support roller element immerses in the blocking position.

In a particularly preferred embodiment, the support rolling elements are cylindrically formed. The support rollers can therefore be formed as rollers. Alternatively, however, it would also be conceivable to use spheres as rolling elements.

In a further development of the invention, the electromagnet device has several electromagnets grouped around the coupling rod, which, when energized, hold the support sleeve together in the support position.

In some embodiments, the electromagnets are each spring-loaded, in particular coupled on the underside with a recoil spring, which is compressed in the blocking position of the blocking unit and which, in the release position, moves said blocking unit out if its original position when deactivating the electromagnets, wherein an associated position sensor can detect a change in position.

In a particularly preferred manner, the release spring means has a plurality of release springs grouped around the coupling rod, which release springs move the support sleeve upon deactivation of the electromagnet device together into the release position. Conveniently, the trigger springs and the electromagnets are arranged in the circumferential direction offset to each other.

In a further development of the invention, the blocking sleeve has an inner sleeve portion formed with the counter-stop, which inner sleeve portion surrounds the coupling rod concentrically and is immersed in an annular space between a cylindrical housing inner section and the coupling rod, and wherein the blocking sleeve has a sleeve portion, which surrounds the housing inner section in a concentric manner, and wherein the receiving space for the blocking rolling elements is formed on the inner wall of said inner section.

In a particularly preferred manner, recoil agents are provided for returning the blocking unit against the spring force of the spring device from the blocking position into the release position. The recoil agents may have a mechanical, fluidic or electrical recoil drive for returning the blocking unit to the release position. For example, the recoil drive can be formed as a servo motor. However, other types of recoil drives are also possible, such as a hydraulic or pneumatic drive.

Some embodiments provide a damping device for damping the exit movement of the blocking unit from the blocking position into the release position when triggering the security function. Conveniently, the damper is designed as an oil damper. The damper conveniently has two oil chambers connected by a throttle, wherein hydraulic oil is displaced from one oil chamber to the other for triggering a damping function.

In a further development of the invention, a retaining device for retaining the support rolling elements against radial movement to the outside is provided in the blocking position of the blocking unit. Since the receiving space of the blocking sleeve is removed because the blocking unit was triggered and is in the release position, there is the need to hold back the support roller elements.

In a particularly preferred manner, the retaining device has a retaining element assigned, in particular, to the respective radially outer support rolling element of a respective support rolling element group, which outer support rolling element is movably arranged between a retaining position, retaining the assigned support roller elements, and a non-use position. Conveniently, the retaining member is spring-loaded and is supported by a recoil spring, which presses the retaining member such that it abuts the radially outer support rolling element in the release position of the support sleeve or in the release position of the blocking device.

Some embodiments of the invention further discloses a drive unit having a linear drive and a safety device, wherein the safety device is characterized according to any of claims 1 to 16.

Further, some embodiments of the invention comprise a valve, in particular a process valve, having a valve fitting and a drive unit, wherein the drive unit is formed according to claim 17.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is shown in the drawings and is explained in more detail below, in which:

FIG. 1 shows a schematic representation of a preferred embodiment of the safety device according to the invention in the longitudinal section, wherein the blocking unit is in the release position,

FIG. 2 shows a schematic representation of the safety device of FIG. 1, wherein the blocking unit is in the blocking position when the safety function is triggered,

FIG. 3 shows a schematic representation of the detail X from FIG. 1,

FIG. 4 shows an enlarged representation of the detail X from FIG. 1, when returning the support sleeve from the release position to the support position,

FIG. 5 shows an enlarged representation of the detail Y from FIG. 2 and

FIG. 6 shows a circuit diagram of an electronic circuit of the electrical interruption (electronic safety solution).

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 to FIG. 6 show a preferred embodiment of the safety device according to the invention. The safety device is in the exemplary case part of a valve (not shown), in particular of a process valve, and is switched on there between a valve drive in the form of a linear drive (not shown) and the valve fitting (not shown). The valve drive may be, for example, an electric or fluidic, in pneumatic linear drive. The linear drive has an output member (not shown), which, in the case of a fluid linear drive, can be the piston rod of a work cylinder, for example, which piston rod in turn is connected to a drive piston, which is moveable back and forth by fluid pressure operation in a cylinder housing.

The output member of the linear drive is coupled with a coupling rod, which is part of the safety device. The coupling rod can also be called a spindle in the case of a process valve.

The valve also has a valve fitting (not shown), which can also be referred to as a valve housing. In the valve housing, a flow channel extends between an input and an output. In the flow channel, there is a flow opening between the input and the output, which is surrounded by a valve seat. A valve member is assigned to the valve seat, which again is connected to the coupling rod.

The valve member is movable by means of a stroke of the coupling rod between a locking position, in which the valve member is fluid-tightly attached to the valve seat and an open position in which the valve member is lifted off the valve.

The stroke of the coupling rod is generated by the valve drive.

The safety device is therefore switched on in the exemplary case between the valve drive and the valve fitting.

As shown in FIG. 1 and FIG. 2, the safety device has a housing, which is linearly movably penetrated by the coupling rod.

The housing has a sleeve-shaped outer section, which is equipped with a lower mounting flange at its lower end and with an upper mounting flange at its upper end. The lower mounting flange of the housing is attached to a disc-shaped magnetic housing which also belongs to the housing, which magnetic housing accommodates the electromagnet device described below in more detail. The magnetic housing is again connected to a socket flange, which is also linearly movably penetrated by the coupling rod. The safety device can be mounted via the socket flange, for example, to a mounting interface of the valve fitting (not shown) of the valve.

The upper fastening flange forms, in particular with its annular inner shoulder, an upper stop for a blocking unit described in more detail below, which upper stop prevents the blocking unit from extending from out of the housing when the safety function is triggered.

As shown in FIG. 1 and FIG. 2, the housing has an inner housing section, which is consecutively enclosed by the housing section. The inner housing section is also formed as a sleeve. Between the outer wall of the inner housing section and the inner wall of the housing outer section, a ring-shaped clearance is formed, in which an outer sleeve section of a blocking sleeve of the blocking unit is linearly movably accommodated.

The axial extension of the inner housing section is lower than the axial extension of the outer housing section. At the sheath surface of the inner housing section, a ring shoulder is formed, which forms an abutment area for a spring of a spring device, said spring being described in more detail below.

The inner wall of the inner housing section protrudes radially to the outside in the area of its upper end, thereby forming the outer wall of a chamber which is described in more detail below.

As already mentioned, the safety device comprises a blocking unit which is linearly movably penetrated by the coupling rod, which blocking unit is relatively movable with respect to the housing between a blocking position blocking a stroke of the coupling rod (FIG. 2) and a release position allowing a linear movement of the coupling rod (FIG. 1).

The main component of the blocking device is a blocking sleeve having the already mentioned outer sleeve section, which is accommodated in the space between the inner housing section and the outer housing section such as to linearly pass the outer sleeve section. The outer sleeve section has on its sheath surface a ring shoulder which forms an upper counter-stop, which abuts at the upper stop on the housing outer cut when triggering the safety function and thus prevents the blocking sleeve from extending out of the housing. In the area of the lower end of the outer sleeve section of the blocking sleeve, there is a ring-shaped receiving chamber at the inner wall, in which a support rolling element, which is described in more detail below, is at least partially immersed.

At the top of the blocking sleeve, a sleeve flange is attached to the outer sleeve section, to which in turn a linear drive can be docked. The sleeve flange further establishes a connection to an inner sleeve section of the blocking sleeve. On the inside of the sleeve flange, another ring shoulder is formed, which forms a further installation surface for the spring of the spring means. The inner sleeve section is linearly movably accommodated in an annular clearance formed by the inner wall of the inner housing section and the outer wall of the coupling rod.

As shown in FIG. 1 and FIG. 2, there is a ring shoulder on the coupling rod, which forms a stop. The stop on the coupling rod corresponds to a counter-stop on the inner sleeve section, which is formed by a final diameter reduction of the through opening of the inner sleeve portion.

As the summary of FIG. 1 and FIG. 2 shows, the stop and counter-stop are aligned in the release position with axial distance to each other, thereby allowing a stroke movement of the coupling rod. In the blocking position, which is shown in FIG. 2, the stop on the coupling rod and the counter-stop on the inner sleeve section are in contact with each other, whereby a blockage of the coupling rod is caused, thereby preventing a stroke of the coupling rod.

As shown in particular in FIG. 1 and FIG. 2, the outer wall of the inner sleeve portion of the blocking sleeve forms the inner wall of the chamber described in more detail below.

The safety device also comprises a locking device for locking the blocking unit in the release position, wherein the locking device has locking rolling elements accommodated in the housing and one support sleeve which is linearly movably penetrated by the coupling rod.

As shown by the summary of FIG. 1 and FIG. 2 as well as 4 and 5, the support sleeve passes movably between a support position (FIG. 1) and a release position (FIG. 2). In the support position, the support rolling elements are held radially to the outside, engaged in a locked manner with the blocking unit in the locking position, while allowing a retracting of the support rolling elements radially to the inside out of the locking engagement with the blocking unit in the release position.

The support sleeve has a ring-shaped support sleeve reception space on its sheath surface, which space acts together with the receiving space at the sleeve inner portion of the blocking sleeve in the release position, such that the annular support sleeve receiving space is facing the annular receiving space. At its underside, the support sleeve disc-shaped cover section or impact flange with a larger diameter, compared to the rest of the support sleeve, which flange acts together with the trigger springs of a trigger spring device, said trigger spring being described in more detail below.

The locking device has a plurality of support rolling element groups grouped around the circumference of the support sleeve, each having a plurality of support rolling elements, in this exemplary embodiment, three support rolling elements. The support rolling elements are formed in the exemplary embodiment as support rollers. The support rolling elements are arranged successively in the radial direction and therefore have an inner support rolling element, a medium support rolling element and an outer support rolling element for each support rolling element group.

As shown in FIG. 2, the support rolling elements are successively staggered in the blocking position, also in height direction or axial direction. In any case, the inner support rolling element is immersed in the annular support sleeve receiving space both in the blocking position as well as in the release position. However, the outer support rolling element is only immersed in the locking release position in the annular receiving room at the sleeve inner section of the blocking sleeve, whereas it is displaced radially to the inside in the blocking position shown in FIG. 2.

The safety device also comprises an electromagnet device, which, when energized, holds the support sleeve at the support position contrary to the recoil force of at least one trigger spring, such that in the event of a power failure, the holding function can be reversed and the support sleeve can be moved by means of at least one release spring into the release position, thereby allowing the blocking unit to be transferred to the release position by means of the spring device.

In the exemplary embodiment, a plurality of electromagnets are grouped around the coupling rod in the magnetic housing, which electromagnets hold, when energized, the support sleeve in the support position. When energized, the support sleeve is therefore held in the support position, contrary to the spring force of the trigger springs.

The trigger spring device has a plurality of trigger springs grouped around the coupling rod which hold the support sleeve in the release position when deactivating the electromagnet device. As shown in particular in FIG. 1, several cylindrical receiving spaces grouped around the coupling rod are formed in the magnetic housing, in which the assigned trigger springs are accommodated.

The safety device also includes a retaining device for retaining the support rolling elements against movement radially to the outside in the blocking position of the blocking unit, when moving the receiving space upwards on the inner sleeve section of the blocking sleeve.

As shown in FIG. 3 to FIG. 5, the retaining device has a retaining member for each support rolling element group, which retaining member is movably arranged between a retaining position retaining the assigned support rolling element and a non-use position. A recoil spring is assigned to the retaining members, which is on the one hand at the bottom of the retaining member and on the other hand is supported on the socket flange. As shown in particular in FIG. 3 and FIG. 5, a carrier protruding radially to the outside is provided at the retaining member, for example in the form of a screw, which is acted upon by the outer sleeve section when returning the blocking unit from the blocking position to the release position, that is, the lower edge of the sleeve section comes into contact with the carrier, thereby pressing back the retaining member when in contact with the recoil spring. When triggering the safety function, the blocking unit is moved to the blocking position, thereby moving the blocking sleeve upwards, and whereby the recoil spring moves the retaining member such that it is in abutment with the outer support rolling element. The top of the retaining member can be attached to the shape of the attached support rolling element, to be adapted, for example, to the cylinder shape of the support roller.

As shown in FIG. 6 by means of a circuit diagram, a position detection device is provided, with which the position of the electromagnets of the electromagnet device can be detected in order to receive feedback on whether the electromagnets are activated, i.e. energized or deactivated. For this purpose, the electromagnets are mounted in the magnetic housing and are supported from the underside by a recoil spring (FIG. 1). In the activated state of the electromagnets, the support sleeve is tightened and is located in its support position, thereby pushing back the trigger springs and whereby the electromagnets also push back the reset springs. After triggering the safety function, the support sleeve moves away from the electromagnets, since the trigger spring press the support sleeve upwards into the release position. This allows the recoil springs to push the electromagnets upwards, wherein this position change is detected by means of a position sensor (not shown).

The safety device also includes recoil agents for returning the blocking unit from the blocking position to the release position against the spring force of the spring device. In the example shown, the recoil means include an electric recoil drive, for example in the form of a servo motor, which ensures that the blocking sleeve is pushed back against the spring force of the spring of the spring device.

The safety device also comprises a damping device, which is designed in the example as a hydraulic damping device.

As already described above, a chamber is formed by the inner wall of the inner housing section and the outer wall of the inner sleeve section, which can be filled with hydraulic oil.

As shown in FIG. 1, a second smaller chamber is formed below the first chamber, namely only if the blocking sleeve is in the release position, i.e. the blocking sleeve is retracted and locked. The two chambers are interconnected by a throttle (not shown). When triggering the safety function, hydraulic oil is therefore transferred from the second chamber via the throttle into the first chamber which triggers a damping function. The hydraulic oil contained in the first chamber then partially flows into a displacement chamber or equalization chamber (not shown).

In normal operation, the blocking unit is driven in and locked in the release position, which is shown in FIG. 1. In the release position, the stop and the counter-stop are in the axial direction of each other, thereby allowing a lifting motion of the coupling rod within the resulting stroke. The locking of the blocking unit is achieved by energizing the electromagnets. If the electromagnets are activated, i.e. energized, these together hold the support sleeve in the support position.

Crucially, the support rolling elements of the support rolling element group are located in the locking position. This is achieved by the fact that the ring-shaped support sleeve receiving space and the annular receiving space are opposite each other at the outer sleeve section 34 of the blocking sleeve. In this position, the outer support rolling element immerses in the receiving room at the blocking sleeve. At the same time, the inner support rolling element is immersed in the annular support sleeve receiving space. Although the spring of the spring device strives to push the blocking sleeve out of the housing, this is not possible, as the support rolling elements are engaged with each other and the outer support rolling element prevents the blocking sleeve from passing by said outer support rolling element. The recoil force of the spring has an effect on the outer support rolling element, then on the middle support rolling element and then on the inner support rolling element, which, however, also receives its support, since the support sleeve is tightened and is in the support position.

In the event of a power failure, the electromagnets are deactivated, causing their holding force for the support sleeve to be lost.

In this case, the trigger springs presses the support sleeve upwards in its release position, as it is shown in FIG. 2. Since the annular support sleeve receiving space has an axial extension that is larger than the axial extension of the inner support rolling elements, the support sleeve can move past the inner support rolling mem. If the support sleeve then comes into contact with the support rolling element on the inner ring shoulder of the support sleeve receiving space, said support rolling element is moved upwards with the support sleeve, thereby creating free space for the middle support-rolling element. The middle support rolling element can then tilt to some extent radially to the inside, thereby making room for the outer support rolling element, which can also move radially to the inside. This reverses the locking of the blocking unit, such that the spring force of the strongly dimensioned spring of the spring device pushes the blocking sleeve upwards out of the housing until the upper counter-stop on the outer sleeve section abuts the upper stop on the outer housing section.

At the same time, the retaining device is activated, and the retaining members are moved upwards by the recoil springs to the assigned outer support rolling elements, thereby holding the outer support rolling element.

When extending the blocking sleeve, the hydraulic oil located in the second chamber is displaced into the first chamber, thereby triggering a damping function which prevents the blocking sleeve from suddenly ejecting as a result of the high spring force of the spring of the spring device.

In the blocking system shown in FIG. 2, the blocking sleeve is unlocked and extended from the housing. In this state, the counter-stop on the sleeve section of the blocking sleeve abuts the stop arranged at the coupling rod, which prevents lifting of the coupling rod downwards. This allows, for example, a coupled valve member to be driven into a defined open position.

The returning of the blocking unit from the block position shown in FIG. 2 to the release position shown in FIG. 1 proceeds as follows:

By means of a servo motor, a force is exerted on the blocking sleeve, thereby retracting the blocking sleeve contrary to the force of the spring device into the housing. When the blocking sleeve is retracted, the sleeve outer section and also the sleeve inner section are moved downwards.

As shown in particular in FIG. 4, an actuation element, which is particularly adjustable in height, is arranged at the bottom of the inner sleeve portion, for example arranged in the form of a screw, which, when retracting the blocking sleeve, comes into contact, with the upper end of the support sleeve, which is still in the release position. The actuation element therefore pushes the support sleeve against the spring force of the trigger springs back into the support position and in the range of the magnet attraction of the electromagnets, which are activated and hold the support sleeve in the support position. At the same time, the retaining members are pressed down by the abutment of the inner edge of the outer sleeve section against the spring for of their recoil springs and the receiving space, in the area of the outer sleeve section, comes into the area of the outer support rolling element, which then immerses in the annular receiving room.

After shifting the support sleeve from its release position to the support position, the blocking sleeve can then move upwards to some extent, thereby reaching the support position of the support rolling elements.

FIG. 6 shows a schematic circuit diagram of an electronic circuit for the control of electronic interrupting (electronic safety solution). The circuit is part of the safety device.

This is a single transistor circuit, which is fed by the quiescent current of the electric actuator in the form of the servo motor.

The electronic circuit comprises a circuit in which the electromagnetic device is switched on. In the circuit, two switches in the form of transistors, in particular non-transistors, are switched on. The first transistor is connected to a higher-level controller, especially a PLC control. If the output is inert, the switch is closed. The second transistor is a redundant safety contact. If the output of the second transistor is energized, i.e. high, the switch is closed. The electromagnets of the electromagnet device are only activated if the two outputs of the transistors are high. The electromagnets are connected in parallel, so that they switch at the same time.

The two output signals are controlled by a current measurement and detection circuit. In total, there are two possible situations. The first situation is called SPIKE or peak, the other situation is called ALIVE or error. The situation is SPIKE if a switch-on peak is detected in particular in the form of a 0.5 s high pulse. This is basically independent of the number of actual switching electromagnets. Three electromagnets are shown as examples. Of course, it is possible to operate the safety device with more than three parallel connected electromagnets.

In particular, the switch-on peak is considerably higher than the rated current. Thus, if the current is well above the normal operating intake, the SPIKE output is, for example, 0.5 s high. A switch-on peak results only if metal is attached to the magnet, i.e. if the electromagnets abut the metal base flange against the spring force of the recoil spring. This is the case when the blocking unit is locked (FIG. 1).

The situation is ALIVE (error) if not all electromagnets are activated, for example only one or two or, as shown in the circuit diagram by the reference signs (one not activated magnet) and (two not activated magnets). However, the situation can also be detected that, although all three electromagnets are activated, they are not pushed back to their basic position by the recoil force of the recoil spring. In this case, there is no metal attached to the electromagnet, but an air gap is formed, so that the measured value of the current is significantly lower. In this case, there is no switch-on peak. 

What is claimed is:
 1. A safety device for detachably locking the drive member of a linear drive comprising: a coupling rod that can be coupled with the output element of the linear drive, a housing penetrated linearly movably by the coupling rod, a blocking unit penetrated linearly movably by the coupling rod which is relatively movable with respect to the housing between a locking position blocking the stroke of the coupling rod and a release position enabling the linear movement of the coupling rod, a spring device for prestressing the blocking unit in the blocking position, a locking device for locking the blocking unit in the release position, wherein the locking device has locking rolling elements accommodated in the housing and a support sleeve penetrated linearly movably by the coupling rod wherein the support sleeve is movable between a support position, in which the support rolling elements are held radially to the outside with the blocking unit in locking engagement and a release position, allowing a retracting of the support rolling elements radially to the inside, out of the engagement with the blocking unit, an electromagnet device which, when energized, holds the support sleeve in the support position against the recoil force of at least one trigger spring of a trigger spring device, in such a way that in the event of a power failure, the holding function can be reversed and the support sleeve is moved to the release position by means of at least the one trigger spring, thereby allowing the blocking unit to be transferred to the blocking position by means of the spring device.
 2. The safety device according to claim 1, characterized by the fact that a stop on the coupling rod and a counter-stop on the blocking device are formed which are arranged, in the release position, with an axial distance to each other determining the stroke of the coupling rod and abut each other in blocking position resulting in the locking of the output member.
 3. The safety device according to claim 1, characterized in that the blocking unit has a blocking sleeve penetrated by the coupling rod which supports the locking rolling elements, in the release position radially to the outside and holds them in the locking position.
 4. The safety device according to claim 3, characterized in that the blocking sleeve has an annular receiving space in which an assigned support rolling element is immersed in the locking position.
 5. The safety device according to claim 1, characterized in that a plurality of support rolling elements groups grouped around the circumference of the support sleeve are provided having each at least one support rolling element.
 6. The safety device according to claim 5, characterized by the fact that the support rolling element groups each have a plurality of support rolling elements arranged successively in radial direction.
 7. The safety device according to claim 5, characterized in that the support rolling elements of each support rolling element group in the release position of the support sleeve are staggered in the height direction.
 8. The safety device according to claim 1, characterized in that the support sleeve has an outer wall on which a support sleeve receiving space is formed which acts together with the receiving space of the blocking unit in the support position, in which support sleeve receiving space a support roller element is immersed in the support position.
 9. The safety device according to claim 1, characterized in that the support rolling elements are formed cylindrically.
 10. The safety device according to claim 1, characterized in that the electromagnet device has a plurality of electromagnets formed around the coupling rod which hold the support sleeve together in the support position when energized.
 11. The safety device according to claim 1, characterized in that the release spring device has a plurality of release springs grouped around the coupling rod which together move the support sleeve into the release position when deactivating the electromagnetic device.
 12. The safety device according to claim 1, characterized in that the blocking sleeve has an inner sleeve section formed with the counter-stop, which inner sleeve section surrounds the coupling rod concentrically and which is immersed in an annular space between a cylindrical inner housing section of the housing and the coupling rod, and wherein the blocking sleeve has an outer sleeve section, which surrounds the inner housing section concentrically and wherein, at its inner wall, the receiving space for the locking rolling elements is formed.
 13. The safety device according to claim 1, characterized by recoil means for returning the blocking unit against the spring force of the spring device from the blocking position to the release position.
 14. The safety device according to claim 13, characterized by the fact that the recoil means have a mechanical, fluid or electrical reset drive for returning the blocking unit in the release position and preferably wherein the recoil drive is formed as a servo motor.
 15. The safety device according to claim 1, characterized in that a retaining device is provided for retaining the support rolling elements against the movement radially to the outside in the blocking position of the blocking unit.
 16. The safety device according to claim 15, characterized by the fact that the retaining device has a retaining member assigned to a respective support-rolling element group, in particular to the radially outer support rolling element, which retaining member is movable between a retaining position retaining the assigned support rolling element and a non-use position.
 17. A drive unit comprising a linear drive and the safety device according to claim
 1. 18. A process valve comprising a valve fitting and the drive unit according to claim
 17. 